swelling vs nub

swelling and nub both are nouns.

Word	Noun	Adjective	Verb	Adverb
swelling	Yes	No	No	No
nub	Yes	No	No	No

As nouns, nub is a hyponym of swelling; that is, nub is a word with a more specific, narrower meaning than swelling:

swelling: something that bulges out or is protuberant or projects from its surroundings
nub: a small lump or protuberance

Other hyponyms of swelling include frontal eminence, occipital protuberance, belly, caput, mogul, nubble, snag, wart.

swelling (noun)	nub (noun)
the increase in volume of certain substances when they are heated (often accompanied by release of water)	the choicest or most essential or most vital part of some idea or experience
something that bulges out or is protuberant or projects from its surroundings	a small piece
an abnormal protuberance or localized enlargement	a small lump or protuberance